1. Field of the Invention
The present invention relates to a liquid ejection head to be used in a liquid ejection apparatus for ejecting liquid such as ink to form an image or perform recording, and to a method of producing the liquid ejection head.
2. Description of the Related Art
A liquid ejection head forms an image by ejecting liquid droplets. The liquid droplets are ejected by heating the liquid by an energy-generating element including a heat generating resistor, thereby causing film boiling in the liquid. Alternatively, a piezoelectric element may be used sometimes to eject the liquid droplets, or a method involving irradiating the liquid with an electromagnetic wave generated by a laser or the like is also sometimes employed. Such a liquid ejection head is generally mounted on a recording apparatus main body. The liquid ejection head is controlled and driven by an electrical signal supplied from the recording apparatus main body to form an image. Therefore, in order to form an image by the liquid ejection head, electrical communication is necessary between the recording apparatus main body and the liquid ejection head.
In order to achieve the electrical communication, the liquid ejection head includes an electrical wiring board for electrically connecting the energy-generating element and the recording apparatus main body. The electrical wiring board includes an electrical signal input portion including conductive contact pads, and the recording apparatus main body includes contact pins to be electrically connected to the contact pads, respectively. The contact between the contact pad and the contact pin enables the electrical communication. As disclosed in Japanese Patent Application Laid-Open No. 2007-320229, the electrical wiring board is formed of a flexible wiring board in which a plurality of electrical wiring lines are arranged in a single layer, and the contact pads are provided directly on the flexible wiring board. In order to reduce the size of the electrical signal input portion, a multilayer wiring board in which a plurality of electrical wiring lines are arranged in a plurality of layers is sometimes connected to the flexible wiring board, and the contact pads are formed on the multilayer wiring board. The electrical wiring board is bent along two surfaces of a housing of the liquid ejection head at the stage of producing the liquid ejection head, and is crimped around the electrical signal input portion (for example, at four positions).
The main portion of the electrical wiring board, in particular, a bent portion is made of a flexible material such as a flexible wiring board, but it is difficult to bend the electrical wiring board completely along the shape of the housing. Therefore, when the electrical wiring board is bent, lifting may occur near the bent portion. FIG. 12A is a perspective view illustrating the relationship between a liquid ejection head 1 and a sheet P on which an image is to be recorded, and FIG. 12B is a sectional view taken along the line 12B-12B of FIG. 12A. An electrical wiring board 5 is first bonded to a first surface 33 of a housing 6, which is located on the same side as ejection orifices, and is then bent by about 90° along the corner of the housing 6 to be fixed along a second surface 34 of the housing 6. At this time, lifting C occurs near a bent portion 21 due to the bending rigidity of the electrical wiring board. This tendency is remarkable in an electrical wiring board having a large area in a region other than the electrical signal input portion or in a wide electrical wiring board. The lifting of the electrical wiring board occurs not only during production but also due to heat after usage and change over the years. Such lifting near the bent portion 21 leads to increase in dimension of the liquid ejection head in the traveling direction (hereinafter referred to as “Y direction”) of the sheet P (hereinafter referred to as “Y direction dimension Dy”) as illustrated in FIG. 12B.
The increase in the Y direction dimension Dy causes the following problems. As illustrated in FIGS. 12A and 12B, on both sides of the liquid ejection head 1 in the Y direction, sheet pressing rollers 61a and 61b are respectively provided. The sheet pressing rollers 61a and 61b are located near the housing 6 of the liquid ejection head 1 in order to satisfactorily press the sheet P in the vicinity of the ejection orifices. Therefore, the sheet pressing roller 61a on the side of the second surface 34 of the housing 6 of the liquid ejection head 1 may interfere with the electrical wiring board 5 protruding due to the lifting. In order to avoid this interference, it is necessary to separate the sheet pressing roller 61a away from the second surface 34 as indicated by the broken lines. In this case, an interval L between the two sheet pressing rollers 61a and 61b increases. The increase in the interval L causes problems such as printing failure and paper jam due to reduction of the effect to press the sheet by the sheet pressing rollers 61a and 61b. The paper jam often occurs if the sheet is unsatisfactorily pressed particularly when the sheet enters the space below the liquid ejection head 1 during sheet feeding. Further, in a general small-sized recording apparatus, with increasing printing speed in recent years, the longitudinal direction (Y direction) dimension of the ejection orifice array tends to increase. In such a recording apparatus, as the Y direction dimension of the liquid ejection head increases, accordingly, the interval between the sheet pressing rollers also tends to increase, and hence the interval between the sheet pressing rollers further increases due to the occurrence of the above-mentioned lifting.
In order to reduce the height of the lifting, it is also conceivable to crimp and fix the electrical wiring board while strongly pulling the electrical wiring board. In this case, however, the electrical wiring board is fixed under a tensioned state, and hence a crimped part of the electrical wiring board may be cracked after the tension is released, or another part thereof may be wrinkled. Therefore, the above-mentioned problems cannot be solved.